PDGFs are essential for the development and normal functioning of many tissues and cell types. Although some targets of PDGF signaling have been identified, exactly how PDGF mediates the complex processes of development on a cellular level is still unknown. Recently, several genes downstream of PDGF have been identified using a novel gene trap screen in ES cells. Experiments in the first project will use null phenotypes, expression patterns, and epistasis experiments to determine the roles of individual genes in the development and PDGF mediated control of specific tissues. PDGF receptors activate multiple signaling pathways through a unique contingent of downstream effector proteins. Experiments in the second project will use microarray analysis of expression patterns downstream of specific effectors in order determine the contribution of each pathway to PDGF signaling. This work will address conflicts in the field as to whether individual pathways control specific biological effects in the cell, or if these pathways are additive, and it is the summation of the intensity of these collective pathways that transmits a unique signal for a given receptor.